Some service members say they have no other choice because the Defence Department's method of estimating body fat is weeding out not just flabby physiques but bulkier, muscular builds.

Some fitness experts and doctors agree, and they are calling for the military's fitness standards to be revamped.

Defence officials said only a fraction of those who exceed body fat limits perform well on physical fitness tests.

The checks are designed to ensure troops are ready for the rigours of combat. Pentagon officials said the military does not condone surgical alterations to pass the test, although liposuction is not prohibited.

-AP

The Defence Department uses what is called a "tape test" to make a body fat estimate by taking measurements of the waist and neck.

Those who fail are ordered to spend months in a vigorous exercise and nutrition programme, which Marines call the "pork chop platoon" or "doughnut brigade." Even if they later pass, failing the test once can halt promotions for years, service members say.

Failing three times can be grounds for getting kicked out, military officials say.

The number of Army soldiers booted for being overweight has jumped tenfold in the past five years from 168 in 2008 to 1,815. In the Marines, the figure nearly doubled from 102 in 2010 to 186 in 2011 but dropped to 132 last year.

The Air Force and the Navy said they do not track discharges tied to the tape test.

Still, service members say they are under intense scrutiny as the military trims its ranks amid budget cuts and as the Afghanistan war winds down.

Dr Michael Pasquale of Aloha Plastic Surgery in Honolulu said his military clientele has jumped by more than 30% since 2011, with about a half-dozen service members coming in every month.

"Some see this as unethical but I say, 'What? It's liposuction, for God's sake,'" the former soldier said. "They have to worry about their careers. With the military downsizing, it's putting more pressure on these guys."

Some go on crash diets or use weights to beef up their necks so they are in proportion with a larger waist. Dr Pasquale said liposuction works for those with the wrong genetics.

Fitness expert Jordan Moon said there is no reliable, economical way to measure body fat, and troops should be judged more by physical performance so they're not feeling forced to go to such lengths to save their careers.

Studies have shown a correlation between waist size, body fat and physical endurance, military officials say, and the tape test is the best, most cost-effective tool available, with a margin of error of less than 1%.